1. Field of the Invention
The present invention relates to a nitride-based semiconductor light emitting diode (LED). In the nitride-based semiconductor LED, when a flip-chip bonding process is performed, a light-emitting region of a chip can be prevented from being damaged by an excessive load of a bump ball which is more than a critical value.
2. Description of the Related Art
Since nitride-based semiconductors such as GaN and the like have excellent physical and chemical properties, they are considered as essential materials of light emitting diodes, for example, light emitting diodes (LEDs) or laser diode (LDs). Particularly, the nitride-based semiconductor LED can generate blue or green light and ultraviolet light, and the brightness thereof has rapidly increased due to the technical development. Therefore, the nitride-based semiconductor LED is applied to a full-color display board, a lighting device or the like.
The nitride-based semiconductor LED is manufactured of nitride semicondcutor materials having a compositional formula of InXAlYGa1-X-YN (0≦X, 0≦Y, X+Y≦1), in order to obtain blue or green light.
Nitride-based semiconductor crystal is grown on a substrate for growing single crystal such as a sapphire substrate, in consideration of lattice matching. Particularly, since the sapphire substrate is an electrically insulating substrate, a finalized nitride-based semiconductor LED has such a structure that both of a p-electrode and an n-electrode are formed on the same surface.
Because of such a structural characteristic, the nitride-based semiconductor LED is actively developed in the form which is suitable for a flip-chip structure.
Hereinafter, a conventional nitride-based semiconductor LED will be described in detail with reference to FIGS. 1 and 2.
FIG. 1 is a diagram illustrating a bonding process of the conventional nitride-based semiconductor LED. The conventional nitride-based semiconductor LED 10 includes a nitride-based semiconductor LED mounted on a sub-mount 200.
The nitride-based semiconductor LED includes a sapphire substrate 101, a light-emitting structure in which an n-type nitride semiconductor layer 103, an active layer 105, a p-type nitride semiconductor layer 107 are sequentially laminated on the sapphire substrate 101, a p-electrode 110a formed on the p-type nitride semiconductor layer 107, and an n-electrode 110b formed on the n-type nitride semiconductor layer 103.
On the surfaces of the sub-mount 200 corresponding to the p-electrode 110a and the n-electrode 110b of the nitride-based semiconductor LED, p-type and n-type lead patterns 201a and 201b, respectively, are formed so as to be electrically connected thereto. Here, the n-electrode 110a and the p-electrode 110b of the nitride semiconductor LED and the n-type and p-type lead patterns 201a and 201b of the sub-mount are electrically bonded to each other through conductive bump balls 300.
Except for portions of the p-electrode 110a and the n-electrode 110b which are electrically connected to the n-type and p-type lead patterns 201a and 201b of the sub-mount, the nitride-based semiconductor LED is protected by a protective film.
In general, a flip-chip bonding process is where a sub-mount and a nitride-based semiconductor LED are electrically connected through a physical load using a conductive bump ball. In such a flip-chip bonding process, the sub-mount and the nitride-based semiconductor LED are separated unless a load more than a critical value is applied. Therefore, a load more than a critical value is required.
In the conventional nitride-based semiconductor LED, however, the conductive bump balls 300 with a load more than a critical value come in direct contact with the p-electrode 110a and the n-electrode 110b of the nitride-based semiconductor LED, that is, a bonding pad, as shown in FIG. 1. Therefore, when a flip-chip bonding is performed, excessive stress is applied to the nitride semiconductor LED, thereby destroying PN junction of the diode or damaging a light-emitting region. FIG. 2 is a photograph showing the problems occurring when the flip bonding process is performed, showing that the light-emitting region is damaged by an excessive load of the conductive bump ball.